用eclipse移动应用开发设计一个计时器，包括main.xml文件和java文件

这里提供一个简单的计时器示例，包括一个主界面的布局文件 `activity_main.xml` 和一个 Java 文件 `MainActivity.java`。

1. `activity_main.xml` 文件：

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <TextView
        android:id="@+id/timerTextView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textSize="30sp"
        android:layout_centerInParent="true"
        android:text="00:00:00" />

    <Button
        android:id="@+id/startButton"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Start"
        android:layout_below="@+id/timerTextView"
        android:layout_marginTop="20dp"
        android:layout_alignParentLeft="true"
        android:layout_marginLeft="40dp" />

    <Button
        android:id="@+id/pauseButton"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Pause"
        android:layout_below="@+id/timerTextView"
        android:layout_marginTop="20dp"
        android:layout_centerHorizontal="true" />

    <Button
        android:id="@+id/resetButton"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Reset"
        android:layout_below="@+id/timerTextView"
        android:layout_marginTop="20dp"
        android:layout_alignParentRight="true"
        android:layout_marginRight="40dp" />

</RelativeLayout>

2. `MainActivity.java` 文件：

import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

import androidx.appcompat.app.AppCompatActivity;

public class MainActivity extends AppCompatActivity {
    private TextView timerTextView; // 显示计时的 TextView
    private Button startButton, pauseButton, resetButton; // 开始、暂停、重置按钮
    private int seconds = 0; // 计时器秒数
    private boolean isRunning = false; // 是否已经开始计时
    private boolean wasRunning = false; // 计时器是否在暂停前运行

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        timerTextView = findViewById(R.id.timerTextView);

        startButton = findViewById(R.id.startButton);
        startButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                startTimer();
            }
        });

        pauseButton = findViewById(R.id.pauseButton);
        pauseButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                pauseTimer();
            }
        });

        resetButton = findViewById(R.id.resetButton);
        resetButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                resetTimer();
            }
        });

        if (savedInstanceState != null) {
            seconds = savedInstanceState.getInt("seconds");
            isRunning = savedInstanceState.getBoolean("isRunning");
            wasRunning = savedInstanceState.getBoolean("wasRunning");
        }

        runTimer();
    }

    // 保存状态以防止屏幕旋转时计时器重置
    @Override
    public void onSaveInstanceState(Bundle savedInstanceState) {
        savedInstanceState.putInt("seconds", seconds);
        savedInstanceState.putBoolean("isRunning", isRunning);
        savedInstanceState.putBoolean("wasRunning", wasRunning);
        super.onSaveInstanceState(savedInstanceState);
    }

    // 开始计时
    private void startTimer() {
        isRunning = true;
    }

    // 暂停计时
    private void pauseTimer() {
        isRunning = false;
        wasRunning = true;
    }

    // 重置计时器
    private void resetTimer() {
        seconds = 0;
        isRunning = false;
        wasRunning = false;
    }

    // 计算时间并更新 TextView
    private void runTimer() {
        final Handler handler = new Handler() {
            @Override
            public void handleMessage(Message message) {
                int hours = seconds / 3600;
                int minutes = (seconds % 3600) / 60;
                int secs = seconds % 60;
                String time = String.format("%02d:%02d:%02d", hours, minutes, secs);
                timerTextView.setText(time);
            }
        };

        Thread thread = new Thread() {
            @Override
            public void run() {
                while (true) {
                    if (isRunning) {
                        try {
                            Thread.sleep(1000); // 休眠 1 秒钟
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                        seconds++;
                    }
                    handler.sendEmptyMessage(0);
                }
            }
        };
        thread.start();
    }

    // 如果计时器在暂停前运行，则在恢复时继续计时
    @Override
    protected void onResume() {
        super.onResume();
        if (wasRunning) {
            isRunning = true;
        }
    }

    // 如果计时器在暂停前运行，则在暂停时停止计时
    @Override
    protected void onPause() {
        super.onPause();
        wasRunning = isRunning;
        isRunning = false;
    }
}

以上就是一个简单的计时器的实现。你可以根据自己的需要对布局和代码进行修改和扩展。还需要添加相关的权限和依赖库，才能正常运行计时器应用。